1. Field of the Invention
The present invention relates generally to digital television and more specifically to the acquisition and display of picture-in-picture video and Electronic Program Guide information on a digital television receiver.
2. Description of the Related Art
The Advanced Television Systems Committee (ATSC) has proposed a digital television standard in which audio and video information will be transmitted in digital form. Digital signals have a number of benefits over traditional analog transmissions, including greater flexibility in the kinds of information that can be transmitted along with audio and video information, ease of compression of broadcast signals to conserve bandwidth, and convenient manipulation of information at the receiving end.
A typical digital television architecture is shown in FIG. 1. On the transmitting side (not shown), digital signals are compressed using the MPEG-2 compression standard and broken up into a packetised elementary stream (PES) that, under the current standard, are combined into packets of data each containing 188 bytes of information. The packets are modulated onto a radio frequency (RF) carrier signal and broadcast. All broadcast signals, each corresponding to a particular television channel, are received through an antenna 13 that passes the signals to a main tuner 1. Main tuner 1 has been tuned by a central processing unit (CPU) 6, according to input from a remote control 5, to select one of the broadcast signals. Main tuner 1, in turn, passes the selected broadcast signal to a digital demodulator 2 where the packets are demodulated from the carrier signal into a byte-aligned baseband signal. The packets of data are then provided to a transport demultiplexor 3.
Transport demultiplexor 3 performs a number of functions. It buffers incoming packets, extracts clock information from them to perform synchronization, and separates and processes audio, video, and data packets. The separated audio and video packets are provided to an MPEG-2 audio/video (A/V) decoder 4, which decompresses the digital video and audio signals and converts them to analog form. The analog video signal is supplied to a graphics overlay 7 that combines the video with on-screen display (OSD) information supplied by CPU 6 and generates a video out signal for display on a screen (not shown).
One problem with this configuration is that, since the digital television has only a single tuner, a viewer cannot tune to different channels at the same time. The ability to simultaneously tune to more than one channel has the advantage of being able to view programs from separate channels at the same time, such as in a picture-in-picture (PIP) format. The PIP format typically takes the form of a smaller video picture displayed within a larger one. A digital television architecture for implementing traditional picture-in-picture processing is shown in FIG. 2. This architecture includes the components of FIG. 1 and additional components dedicated to displaying a program from a second television channel.
Specifically, signals from antenna 13 are sent to a PIP tuner 8 which is tuned to a particular channel by CPU 6. PIP tuner 8 passes the tuned channel to a digital demodulator 9 where packets are demodulated from the carrier signal. The packets of data are then provided to a transport demultiplexor 10 that performs the same finctions described above with reference to transport demultiplexor 3. An MPEG-2 A/V decoder 11 receives audio and video packets from transport demultiplexor 10, which decompresses the digital video and audio signals and converts them to analog form. The analog video signal is supplied to a PIP image processor 12. PIP image processor 12 is a hardware block that performs 2-D filtering and sub-sampling to effectively squeeze the PIP image into a smaller size. PIP image processor 12 sends the image to graphics overlay 7, which combines the main image, the PIP image, and OSD information into a video out signal.
This technique of providing PIP, however, is very costly. One of the most expensive components in a digital television system is the MPEG-2 decoder. In the implementation shown in FIG. 2, two such MPEG-2 decoders are required to achieve a picture-in-picture display.
Moreover, the systems of FIGS. 1 and 2 both have the disadvantage that they can only display Electronic Program Guide (EPG) information contained within the tuned channel. As noted above, the current broadcast standard allows for data packets to be transmitted along with video and audio packets. Certain data packets contain an EPG that is inserted into the digital channel assigned to each broadcaster. The EPG acts as an on-screen guide showing, for example, the names and durations of current and future programs within the tuned channel. Under the current standard, however, there is no requirement that one broadcaster include the program listings of other broadcasters in the EPG transmitted with their channel. In other words, if a viewer tuned to a particular channel and called up the EPG, it would only show the program information for the tuned channel. It would not include EPG information for programs in other broadcast channels. To get this information, the viewer suffers the inconvenience of having to tune to each of the other broadcast channels.
These problems indicate the need for a mechanism that provides users an inexpensive way to achieve picture-in-picture viewing while also allowing accumulation of EPG information from a number of different broadcast channels.